FIG. 7 is a perspective view schematically illustrating a conventional workout assisting instrument 100, publicly available under the brand name “StretchPole Active®,” which is used in a prone posture. The workout assisting instrument 100 is entirely formed by a rubber member made of an elastic material. When a person works out, since a surface of a planar part of the instrument 100 is in full contact with a floor surface, the instrument 100 enables the person to work out in the prone posture in a three-point supporting state, while maintaining an immobile state. That is, a first part 100PA projected from a central part of the instrument 100 contacts a pubis part of the body of the person working out in the prone posture. Further, a second part 100PB extending in an upper right direction at an angle of about 45° from the first part 100PA contacts a protruding part (left anterior superior iliac spine) of a left pelvis part of the person's body. Further, a third part 100PC extending in an upper left direction at an angle of about 45° from the first part 100PA contacts a protruding part (right anterior superior iliac spine) of a right pelvis part of the person's body. By the three-point contact between the parts and the person's body, the workout assisting instrument 100 supports the person's body in the prone posture at the three points. The workout assisting instrument 100 has an advantage as a product in that it is always in a fixed state and immobile during workouts, when the person working out performs the various movements of the workouts while the surface of the planar part of the instrument is in full contact with the floor surface, as described above. The person working out can mainly strengthen their running ability by performing an exercise of raising their limbs in the prone posture with the three-point support as described above.